Module 21: Windows 2000 - Wiley · Module 21: Windows 2000 ... Environmental Subsystems File system...

Silberschatz, Galvin and Gagne 200221.1Operating System Concepts

Module 21: Windows 2000

� History� Design Principles� System Components� Environmental Subsystems� File system� Networking� Programmer Interface


Windows 2000

� 32-bit preemptive multitasking operating system forIntel microprocessors.

� Key goals for the system:✦ portability

✦ security

✦ POSIX compliance✦ multiprocessor support

✦ extensibility

✦ international support✦ compatibility with MS-DOS and MS-Windows

applications.

� Uses a micro-kernel architecture.� Available in four versions, Professional, Server,

Advanced Server, National Server.� In 1996, more NT server licenses were sold than UNIX

licenses


History

� In 1988, Microsoft decided to develop a “new technology”(NT) portable operating system that supported both theOS/2 and POSIX APIs.

� Originally, NT was supposed to use the OS/2 API as itsnative environment but during development NT waschanged to use the Win32 API, reflecting the popularity ofWindows 3.0.


Design Principles

� Extensibility — layered architecture.✦ Executive, which runs in protected mode, provides the basic

system services.

✦ On top of the executive, several server subsystems operatein user mode.

✦ Modular structure allows additional environmentalsubsystems to be added without affecting the executive.

� Portability — 2000 can be moved from on hardwarearchitecture to another with relatively few changes.

✦ Written in C and C++.

✦ Processor-dependent code is isolated in a dynamic linklibrary (DLL) called the “hardware abstraction layer” (HAL).


Design Principles (Cont.)

� Reliability — 2000 uses hardware protection for virtualmemory, and software protection mechanisms foroperating system resources.

� Compatibility — applications that follow the IEEE 1003.1(POSIX) standard can be complied to run on 2000 withoutchanging the source code.

� Performance — 2000 subsystems can communicate withone another via high-performance message passing.

✦ Preemption of low priority threads enables the system torespond quickly to external events.

✦ Designed for symmetrical multiprocessing.

� International support — supports different locales via thenational language support (NLS) API.


2000 Architecture

� Layered system of modules.� Protected mode — HAL, kernel, executive.� User mode — collection of subsystems

✦ Environmental subsystems emulate different operatingsystems.

✦ Protection subsystems provide security functions.


Depiction of 2000 Architecture


� Foundation for the executive and the subsystems.� Never paged out of memory; execution is never

preempted.� Four main responsibilities:

✦ thread scheduling

✦ interrupt and exception handling

✦ low-level processor synchronization✦ recovery after a power failure

� Kernel is object-oriented, uses two sets of objects.✦ dispatcher objects control dispatching and synchronization

(events, mutants, mutexes, semaphores, threads andtimers).

✦ control objects (asynchronous procedure calls, interrupts,power notify, power status, process and profile objects.)

System Components — Kernel


Kernel — Process and Threads

� The process has a virtual memory address space,information (such as a base priority), and an affinity forone or more processors.

� Threads are the unit of execution scheduled by thekernel’s dispatcher.

� Each thread has its own state, including a priority,processor affinity, and accounting information.

� A thread can be one of six states: ready, standby,running, waiting, transition, and terminated.


Kernel — Scheduling

� The dispatcher uses a 32-level priority scheme todetermine the order of thread execution. Priorities aredivided into two classes..

✦ The real-time class contains threads with priorities rangingfrom 16 to 32.

✦ The variable class contains threads having priorities from 0to 15.

� Characteristics of 2000’s priority strategy.✦ Trends to give very good response times to interactive

threads that are using the mouse and windows.

✦ Enables I/O-bound threads to keep the I/O devices busy.

✦ Complete-bound threads soak up the spare CPU cycles inthe background.


Kernel — Scheduling (Cont.)

� Scheduling can occur when a thread enters the ready orwait state, when a thread terminates, or when anapplication changes a thread’s priority or processoraffinity.

� Real-time threads are given preferential access to theCPU; but 2000 does not guarantee that a real-time threadwill start to execute within any particular time limit.


Kernel — Trap Handling

� The kernel provides trap handling when exceptions andinterrupts are generated by hardware of software.

� Exceptions that cannot be handled by the trap handlerare handled by the kernel's exception dispatcher.

� The interrupt dispatcher in the kernel handles interruptsby calling either an interrupt service routine (such as in adevice driver) or an internal kernel routine.

� The kernel uses spin locks that reside in global memoryto achieve multiprocessor mutual exclusion.


Executive — Object Manager

� 2000 uses objects for all its services and entities; theobject manger supervises the use of all the objects.

✦ Generates an object handle✦ Checks security.

✦ Keeps track of which processes are using each object.

� Objects are manipulated by a standard set of methods,namely create, open, close, delete, queryname, parse and security.


Executive — Naming Objects

� The 2000 executive allows any object to be given aname, which may be either permanent or temporary.

� Object names are structured like file path names in MS-DOS and UNIX.

� 2000 implements a symbolic link object, which is similarto symbolic links in UNIX that allow multiple nicknames oraliases to refer to the same file.

� A process gets an object handle by creating an object byopening an existing one, by receiving a duplicated handlefrom another process, or by inheriting a handle from aparent process.

� Each object is protected by an access control list.


Executive — Virtual Memory Manager

� The design of the VM manager assumes that theunderlying hardware supports virtual to physical mappinga paging mechanism, transparent cache coherence onmultiprocessor systems, and virtual addressing aliasing.

� The VM manager in 2000 uses a page-basedmanagement scheme with a page size of 4 KB.

� The 2000 VM manager uses a two step process toallocate memory.

✦ The first step reserves a portion of the process’s addressspace.

✦ The second step commits the allocation by assigning spacein the 2000 paging file.


Virtual-Memory Layout


Virtual Memory Manager (Cont.)

� The virtual address translation in 2000 uses several datastructures.

✦ Each process has a page directory that contains 1024page directory entries of size 4 bytes.

✦ Each page directory entry points to a page table whichcontains 1024 page table entries (PTEs) of size 4 bytes.

✦ Each PTE points to a 4 KB page frame in physicalmemory.

� A 10-bit integer can represent all the values form 0 to1023, therefore, can select any entry in the pagedirectory, or in a page table.

� This property is used when translating a virtual addresspointer to a bye address in physical memory.

� A page can be in one of six states: valid, zeroed, freestandby, modified and bad.


Virtual-to-Physical Address Translation

� 10 bits for page directory entry, 20 bits for page tableentry, and 12 bits for byte offset in page.


Page File Page-Table Entry

� 5 bits for page protection, 20 bits for page frameaddress, 4 bits to select a paging file, and 3 bits thatdescribe the page state. V = 0


Executive — Process Manager

� Provides services for creating, deleting, and usingthreads and processes.

� Issues such as parent/child relationships or processhierarchies are left to the particular environmentalsubsystem that owns the process.


Executive — Local Procedure Call Facility

� The LPC passes requests and results between client andserver processes within a single machine.

� In particular, it is used to request services from thevarious 2000 subsystems.

� When a LPC channel is created, one of three types ofmessage passing techniques must be specified.

✦ First type is suitable for small messages, up to 256 bytes;port's message queue is used as intermediate storage, andthe messages are copied from one process to the other.

✦ Second type avoids copying large messages by pointing toa shared memory section object created for the channel.

✦ Third method, called quick LPC was used by graphicaldisplay portions of the Win32 subsystem.


Executive — I/O Manager

� The I/O manager is responsible for✦ file systems✦ cache management

✦ device drivers

✦ network drivers

� Keeps track of which installable file systems are loaded,and manages buffers for I/O requests.

� Works with VM Manager to provide memory-mapped fileI/O.

� Controls the 2000 cache manager, which handles cachingfor the entire I/O system.

� Supports both synchronous and asynchronous operations,provides time outs for drivers, and has mechanisms forone driver to call another.


File I/O


Executive — Security Reference Manager

� The object-oriented nature of 2000 enables the use of auniform mechanism to perform runtime access validationand audit checks for every entity in the system.

� Whenever a process opens a handle to an object, thesecurity reference monitor checks the process’s securitytoken and the object’s access control list to see whetherthe process has the necessary rights.


Environmental Subsystems

� User-mode processes layered over the native 2000executive services to enable 2000 to run programsdeveloped for other operating system.

� 2000 uses the Win32 subsystem as the main operatingenvironment; Win32 is used to start all processes. It alsoprovides all the keyboard, mouse and graphical displaycapabilities.

� MS-DOS environment is provided by a Win32 applicationcalled the virtual dos machine (VDM), a user-modeprocess that is paged and dispatched like any other 2000thread.


Environmental Subsystems (Cont.)

� 16-Bit Windows Environment:✦ Provided by a VDM that incorporates Windows on Windows.✦ Provides the Windows 3.1 kernel routines and sub routines

for window manager and GDI functions.

� The POSIX subsystem is designed to run POSIXapplications following the POSIX.1 standard which isbased on the UNIX model.


File System

� The fundamental structure of the 2000 file system (NTFS)is a volume.

✦ Created by the 2000 disk administrator utility.✦ Based on a logical disk partition.

✦ May occupy a portions of a disk, an entire disk, or spanacross several disks.

� All metadata, such as information about the volume, isstored in a regular file.

� NTFS uses clusters as the underlying unit of diskallocation.

✦ A cluster is a number of disk sectors that is a power of two.

✦ Because the cluster size is smaller than for the 16-bit FATfile system, the amount of internal fragmentation is reduced.


File System — Internal Layout

� NTFS uses logical cluster numbers (LCNs) as diskaddresses.

� A file in NTFS is not a simple byte stream, as in MS-DOSor UNIX, rather, it is a structured object consisting ofattributes.

� Every file in NTFS is described by one or more records inan array stored in a special file called the Master FileTable (MFT).

� Each file on an NTFS volume has a unique ID called a filereference.

✦ 64-bit quantity that consists of a 48-bit file number and a 16-bit sequence number.

✦ Can be used to perform internal consistency checks.

� The NTFS name space is organized by a hierarchy ofdirectories; the index root contains the top level of the B+tree.


File System — Recovery

� All file system data structure updates are performedinside transactions.

✦ Before a data structure is altered, the transaction writes alog record that contains redo and undo information.

✦ After the data structure has been changed, a commit recordis written to the log to signify that the transactionsucceeded.

✦ After a crash, the file system data structures can berestored to a consistent state by processing the log records.


File System — Recovery (Cont.)

� This scheme does not guarantee that all the user file datacan be recovered after a crash, just that the file systemdata structures (the metadata files) are undamaged andreflect some consistent state prior to the crash..

� The log is stored in the third metadata file at thebeginning of the volume.

� The logging functionality is provided by the 2000 log fileservice.


File System — Security

� Security of an NTFS volume is derived from the 2000object model.

� Each file object has a security descriptor attribute storedin this MFT record.

� This attribute contains the access token of the owner ofthe file, and an access control list that states the accessprivileges that are granted to each user that has accessto the file.


Volume Management and Fault Tolerance

� FtDisk, the fault tolerant disk driver for 2000, providesseveral ways to combine multiple SCSI disk drives intoone logical volume.

� Logically concatenate multiple disks to form a largelogical volume, a volume set.

� Interleave multiple physical partitions in round-robinfashion to form a stripe set (also called RAID level 0, or“disk striping”).

✦ Variation: stripe set with parity, or RAID level 5.

� Disk mirroring, or RAID level 1, is a robust scheme thatuses a mirror set — two equally sized partitions on towdisks with identical data contents.

� To deal with disk sectors that go bad, FtDisk, uses ahardware technique called sector sparing and NTFS usesa software technique called cluster remapping.


Volume Set On Two Drives


Stripe Set on Two Drives


Stripe Set With Parity on Three Drives


Mirror Set on Two Drives


File System — Compression

� To compress a file, NTFS divides the file’s data intocompression units, which are blocks of 16 contiguousclusters.

� For sparse files, NTFS uses another technique to savespace.

✦ Clusters that contain all zeros are not actually allocated orstored on disk.

✦ Instead, gaps are left in the sequence of virtual clusternumbers stored in the MFT entry for the file.

✦ When reading a file, if a gap in the virtual cluster numbers isfound, NTFS just zero-fills that portion of the caller’s buffer.


Networking

� 2000 supports both peer-to-peer and client/servernetworking; it also has facilities for network management.

� To describe networking in 2000, we refer to two of theinternal networking interfaces:

✦ NDIS (Network Device Interface Specification) — Separatesnetwork adapters from the transport protocols so that eithercan be changed without affecting the other.

✦ TDI (Transport Driver Interface) — Enables any sessionlayer component to use any available transport mechanism.

� 2000 implements transport protocols as drivers that canbe loaded and unloaded from the system dynamically.


Networking — Protocols

� The server message block (SMB) protocol is used tosend I/O requests over the network. It has four messagetypes:- Session control

- File

- Printer

- Message

� The network basic Input/Output system (NetBIOS) is ahardware abstraction interface for networks. Used to:

✦ Establish logical names on the network.

✦ Establish logical connections of sessions between twological names on the network.

✦ Support reliable data transfer for a session via NetBIOSrequests or SMBs


Networking — Protocols (Cont.)

� NetBEUI (NetBIOS Extended User Interface): defaultprotocol for Windows 95 peer networking and Windowsfor Workgroups; used when 2000 wants to shareresources with these networks.

� 2000 uses the TCP/IP Internet protocol to connect to awide variety of operating systems and hardwareplatforms.

� PPTP (Point-to-Point Tunneling Protocol) is used tocommunicate between Remote Access Server modulesrunning on 2000 machines that are connected over theInternet.

� The 2000 NWLink protocol connects the NetBIOS toNovell NetWare networks.


Networking — Protocols (Cont.)

� The Data Link Control protocol (DLC) is used to accessIBM mainframes and HP printers that are directlyconnected to the network.

� 2000 systems can communicate with Macintoshcomputers via the Apple Talk protocol if an 2000 Serveron the network is running the Windows 2000 Services forMacintosh package.


Networking — Dist. Processing Mechanisms

� 2000 supports distributed applications via namedNetBIOS,named pipes and mailslots, Windows Sockets,Remote Procedure Calls (RPC), and Network DynamicData Exchange (NetDDE).

� NetBIOS applications can communicate over the networkusing NetBEUI, NWLink, or TCP/IP.

� Named pipes are connection-oriented messagingmechanism that are named via the uniform namingconvention (UNC).

� Mailslots are a connectionless messaging mechanismthat are used for broadcast applications, such as forfinding components on the network,

� Winsock, the windows sockets API, is a session-layerinterface that provides a standardized interface to manytransport protocols that may have different addressingschemes.


Distributed Processing Mechanisms (Cont.)

� The 2000 RPC mechanism follows the widely-usedDistributed Computing Environment standard for RPCmessages, so programs written to use 2000 RPCs arevery portable.

✦ RPC messages are sent using NetBIOS, or Winsock onTCP/IP networks, or named pipes on LAN Managernetworks.

✦ 2000 provides the Microsoft Interface Definition Languageto describe the remote procedure names, arguments, andresults.


Networking — Redirectors and Servers

� In 2000, an application can use the 2000 I/O API toaccess files from a remote computer as if they were local,provided that the remote computer is running an MS-NETserver.

� A redirector is the client-side object that forwards I/Orequests to remote files, where they are satisfied by aserver.

� For performance and security, the redirectors and serversrun in kernel mode.


Access to a Remote File

� The application calls the I/O manager to request that a filebe opened (we assume that the file name is in thestandard UNC format).

� The I/O manager builds an I/O request packet.� The I/O manager recognizes that the access is for a

remote file, and calls a driver called a Multiple UniversalNaming Convention Provider (MUP).

� The MUP sends the I/O request packet asynchronously toall registered redirectors.

� A redirector that can satisfy the request responds to theMUP.

✦ To avoid asking all the redirectors the same question in thefuture, the MUP uses a cache to remember with redirectorcan handle this file.


Access to a Remote File (Cont.)

� The redirector sends the network request to the remotesystem.

� The remote system network drivers receive the requestand pass it to the server driver.

� The server driver hands the request to the proper localfile system driver.

� The proper device driver is called to access the data.� The results are returned to the server driver, which sends

the data back to the requesting redirector.


Networking — Domains

� NT uses the concept of a domain to manage globalaccess rights within groups.

� A domain is a group of machines running NT server thatshare a common security policy and user database.

� 2000 provides three models of setting up trustrelationships.

✦ One way, A trusts B

✦ Two way, transitive, A trusts B, B trusts C so A, B, C trusteach other

✦ Crosslink – allows authentication to bypass hierarchy to cutdown on authentication traffic.


Name Resolution in TCP/IP Networks

� On an IP network, name resolution is the process of convertinga computer name to an IP address.

e.g., www.bell-labs.com resolves to 135.104.1.14

� 2000 provides several methods of name resolution:✦ Windows Internet Name Service (WINS)

✦ broadcast name resolution

✦ domain name system (DNS)✦ a host file

✦ an LMHOSTS file


Name Resolution (Cont.)

� WINS consists of two or more WINS servers that maintaina dynamic database of name to IP address bindings, andclient software to query the servers.

� WINS uses the Dynamic Host Configuration Protocol(DHCP), which automatically updates addressconfigurations in the WINS database, without user oradministrator intervention.


Programmer Interface — Access to Kernel Obj.

� A process gains access to a kernel object named XXX bycalling the CreateXXX function to open a handle to XXX;the handle is unique to that process.

� A handle can be closed by calling the CloseHandlefunction; the system may delete the object if the count ofprocesses using the object drops to 0.

� 2000 provides three ways to share objects betweenprocesses.

✦ A child process inherits a handle to the object.

✦ One process gives the object a name when it is created andthe second process opens that name.

� DuplicateHandle function:

✔ Given a handle to process and the handle’s value asecond process can get a handle to the same object,and thus share it.


Programmer Interface — Process Management

� Process is started via the CreateProcess routine whichloads any dynamic link libraries that are used by theprocess, and creates a primary thread.

� Additional threads can be created by the CreateThreadfunction.

� Every dynamic link library or executable file that is loadedinto the address space of a process is identified by aninstance handle.


Process Management (Cont.)

� Scheduling in Win32 utilizes four priority classes:- IDLE_PRIORITY_CLASS (priority level 4)- NORMAL_PRIORITY_CLASS (level8 — typical for most

processes- HIGH_PRIORITY_CLASS (level 13)

- REALTIME_PRIORITY_CLASS (level 24)

� To provide performance levels needed for interactiveprograms, 2000 has a special scheduling rule forprocesses in the NORMAL_PRIORITY_CLASS.

✦ 2000 distinguishes between the foreground process that iscurrently selected on the screen, and the backgroundprocesses that are not currently selected.

✦ When a process moves into the foreground, 2000 increasesthe scheduling quantum by some factor, typically 3.



� The kernel dynamically adjusts the priority of a threaddepending on whether it is I/O-bound or CPU-bound.

� To synchronize the concurrent access to shared objectsby threads, the kernel provides synchronization objects,such as semaphores and mutexes.

✦ In addition, threads can synchronize by using theWaitForSingleObject or WaitForMultipleObjectsfunctions.

✦ Another method of synchronization in the Win32 API is thecritical section.



� A fiber is user-mode code that gets scheduled accordingto a user-defined scheduling algorithm.

✦ Only one fiber at a time is permitted to execute, even onmultiprocessor hardware.

✦ 2000 includes fibers to facilitate the porting of legacy UNIXapplications that are written for a fiber execution model.


Programmer Interface — Interprocess Comm.

� Win32 applications can have interprocess communicationby sharing kernel objects.

� An alternate means of interprocess communications ismessage passing, which is particularly popular forWindows GUI applications.

✦ One thread sends a message to another thread or to awindow.

✦ A thread can also send data with the message.

� Every Win32 thread has its won input queue from whichthe thread receives messages.

� This is more reliable than the shared input queue of 16-bitwindows, because with separate queues, one stuckapplication cannot block input to the other applications.


Programmer Interface — Memory Management

� Virtual memory:- VirtualAlloc reserves or commits virtual memory.- VirtualFree decommits or releases the memory.

✦ These functions enable the application to determine thevirtual address at which the memory is allocated.

� An application can use memory by memory mapping afile into its address space.

✦ Multistage process.✦ Two processes share memory by mapping the same file into

their virtual memory.


Memory Management (Cont.)

� A heap in the Win32 environment is a region of reservedaddress space.

✦ A Win 32 process is created with a 1 MB default heap.✦ Access is synchronized to protect the heap’s space

allocation data structures from damage by concurrentupdates by multiple threads.

� Because functions that rely on global or static datatypically fail to work properly in a multithreadedenvironment, the thread-local storage mechanismallocates global storage on a per-thread basis.

✦ The mechanism provides both dynamic and static methodsof creating thread-local storage.

Module 21: Windows 2000 - Wiley · Module 21: Windows 2000 ... Environmental Subsystems File system...

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Transcript of Module 21: Windows 2000 - Wiley · Module 21: Windows 2000 ... Environmental Subsystems File system...